Gas discharge display panel for color picture reproduction

ABSTRACT

A gas discharge display panel for efficiently reproducing a color picture having high brightness and high definition. The display panel comprises a plurality of picture elements arranged in matrix. Each picture element is formed by a set of three discharge units reproducing red, green and blue light respectively. Each discharge unit is coupled to a hollow cathode. The hollow cathode of a suitable size is divided into two portions, i.e., a set of display hollow cathodes each of which forms main part of the discharge unit, and a scanning hollow cathode which couples the set of display hollow cathodes and operates for obtaining preparatory discharge. Said two portions of the hollow cathode are jointly operated so as to obtain a large discharge current supply at low voltage and in a small surface area. Thus a practical gas discharge display panel having high density discharge unit arrangement is realized and which is able to increase the luminance by about several tens of per cent more than the conventional one and also being able to be assembled in a simple manner by simplifying the panel construction with unified parts.

United States Patent [1 1 Kamegaya et al.

[ 1 May 6,1975

[ GAS DISCHARGE DISPLAY PANEL FOR COLOR PICTURE REPRODUCTION [75]Inventors: Takeo Kamegaya, Tokyo; Yutaka Imahori; Ryuichi Kaneko, bothof Kawasaki; Minori Yokozawa, Tokyo, all of Japan [73] Assignee: NipponH050 Kyokai, Tokyo, Japan [22] Filed: July 30, 1974 [21] Appl. No.:493,080

[52] US. Cl. 313/188; 313/209; 313/217; 313/419 [51] Int. Cl. H0lj 61/06[58] Field of Search 313/188, 485, 491, 217, 313/209, 220; 315/169 TV[56] References Cited UNlTED STATES PATENTS 3,206,638 9/1965 Moore315/169 TV 3,622,829 11/1971 Watanabe'... 315/169 R X 3,771,008 11/1973Chen et al. 313/188 X Primary ExaminerPa1mer C. Demeo Attorney, Agent,or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A gas dischargedisplay panel for efficiently reproducing a color picture having highbrightness and high definition. The display panel comprises a pluralityof picture elements arranged in matrix. Each picture element is formedby a set of three discharge units reproducing red, green and blue lightrespectively. Each discharge unit is coupled to a hollow cathode. Thehollow cathode of a suitable size is divided into two portions, Le, aset of display hollow cathodes each of which forms main part of thedischarge unit, and a scanning hollow cathode which couples the set ofdisplay hollow cathodes and operates for obtaining preparatorydischarge. Said two portions of the hollow cathode are jointly operatedso as to obtain a large discharge current supply at low voltage and in asmall surface area. Thus a practical gas discharge display panel havinghigh density discharge unit arrangement is realized and which is able toincrease the luminance by about several tens of per cent more than theconventional one and also being able to be assembled in a simple mannerby simplifying the panel construction with unified parts.

10 Claims, 12 Drawing Figures PQENIEE HAY 5 I975 SHEET 1 BF 5 FIG. IPRIOR ART JT44/m PATEIHEUHAY ems SHEET 5 BF 5 Seed Discharge GASDISCHARGE DISPLAY PANEL FOR COLOR PICTURE REPRODUCTION BACKGROUND OF THEINVENTION The present invention relates to a gas discharge display panelfor reproducing color picture. of which panel comprising a display anodeand a scanning anode respectively arranged at front and rear side of itscathode so that the cathode is interposed between these two anodes. Moreparticularly, the present invention relates to an improvement of a gasdischarge display panel comprising a hollow cathode being suitable forcolor picture reproduction.

Various types of display panels using gas discharge have been suggestedheretofore. A gas discharge display panel of the type comprisingdischarge electrodes made of conductive stripes arranged on a surface ofan insulator plate. such as a glass plate. has a drawback in that it isdifficult to obtain a stabilized normal glow discharge in the operationmode of the cathode forming the discharge cell or unit due to its narrowoperation surface emitting the electrons. Furthermore. it tends to causean abnormal glow discharge condition at small discharge current rangeand as the result the discharge voltage tends to rise so thatmisoperation of the discharge cell or fluctuation of the same mightoccur and blackening of inner surface of the panel and loss of thecathode material might result.

Whereas a discharge cell formed by using so-called hollow cathode. whichis made from intermediate insulating plate provided with small holes offor instance cylindrical shape and applied with conductive materials atinner wall surface of the holes to form hollow cathode. is suitable foruse as a gas discharge display panel for color picture reproductionsince it has larger dis charge current when compared with its smallercathode surface and accordingly a higher luminance can be obtained.

For the display of color picture using this type of gas dischargedisplay panel, a known construction as shown in FIG. 1 has been used. InFIG. I. a front panel I made of a transparent insulating material suchas a glass is provided with a plurality of display anodes 2 made ofstripe or belt shaped conductive body arranged vertically and inparallel on the inner surface thereof. A first intermediate insulatingplate 3 made of insulating material such as glass or ceramics isprovided adjacent to the front panel 1. The first intermediateinsulating plate 3 comprises a plurality of matrix shaped dischargespaces 4 each located at a position oppositely facing to one of thedisplay anodes 2. A second intermediate insulating plate 5 made ofinsulating materials such as glass or ceramics is arranged next to saidfirst insulting plate 3. The second insulating plate 5 comprises aplurality of holes 6 also arranged in matrix at a location to face oneof respective discharge spaces 4. The inner surface of the holes 6 ismade conductive and such holes 6 are connected in parallel by conductivestripes in a direction normal to the direction of the display anode 2.The conductive stripes are arranged horizontally in this case. A rearpanel 7 made of like insulating material is arranged at the back side ofthe second intermediate insulating plate 5. The panel 7 is provided witha plurality of slots 8 running in parallel with the display anodes 2 anda plurality of scanning anodes 9 each arranged in the slot 8.

The above-mentioned front panel I, first intermediate insulating plate3, second intermediate insulating plate 5 and the rear panel 7 arestacked in this order and are jointed to form a panel. The edges of thestack are sealed and usually a rare gas is filled inside. The panelconstruction thus formed is excited by applying for instance three phaseac voltage between the scanning anodes 9 and the hollow cathodes 6 toproduce gas discharge plasma. The gas discharge plasma is successivelytransferred along the slots 8 and at the respective transferredpositions a seed discharge is formed in front of the hollow cathode 6 toprepare excitation for the discharge between the hollow cathode 6 andthe display anode 2. By this seed discharge. a gas discharge between thedisplay anode 2 and the hollow cathode 6 is formed. Namely a gasdischarge is formed near the side of the front panel 1. An ultravioletradiation emitted by the gas discharge near the front panel 1 energizesfluorescent materials R. G. B applied. for instance. on the inner wallsurface of the discharge space 4 provided in the first intermediateplate 3 or on the inner surface of the front panel I which emit redlight. green light. blue light. respectively. The light in the threeprimary colors thus produced can be seen through the front panel 1. Ascan be seen from FIG. I. phosphorescent materials each emitting light inone of the three primary colors are applied at suitable positions of thedischarge spaces 4. The three phosphorescent coatings forming a group ofthe three primary colors are arranged to form one picture element. and acolor picture can be reproduced by separately controlling the luminousintensity of each coating.

In color television picture reproduction by using a conventional colortelevision receiver, there is a close relation between the picturequality and the size. pitch. and disposition of the picture elements.and the size of the scanning beam and others. The same relation can beapplied to the gas discharge display panel. Therefore. the size. pitchand allocation of the picture elements should carefully be selected soas to obtain an excellent picture quality.

The conventional construction of the gas discharge display panel asshown in FIG. 1 is not satisfactory for use as a display of colorpicture because of the allocation of the phosphorescent materials of thethree primary colors is not suited for the sight of viewers. Moreparticularly. the pitch of one picture element formed by a set of thethree primary colors differs nearly three times in the horizontaldirection and in the vertical direction which greatly deteriorates thepicture quality. Furthermore. if the scanning is to be made under lineat a time display system for the groups of picture elements in one lineeach of which consisting of the three primary colors. the drivingcircuit arrangement may become very much complicated since each of thehollow cathode 6 and thescanning anode 9 must correspond to onedischarge space 4 and the display anode. Also visible irradiation of thescanning side by the gas discharge may directly be seen from the displayside and moreover. the ultraviolet irradiation produced by the gasdischarge of the scanning side may excite phosphorescent materialprovided in the discharge space 4 to cause luminescence so thatluminance at dark image portion of a picture may increase and whichfurther deteriorates the contrast ratio of the reproduced picture.

SUMMARY OF THE INVENTION The object of the present invention is tomitigate above-mentioned disadvantages of the conventional gas dischargedisplay panel and is to obtain an excellent construction being able toreproduce a high quality color picture.

Another object of the present invention is to provide a gas dischargedisplay panel using hollow cathodes being able to convey much largerdischarge current per unit surface area compared with the conventionaldisplay panel so that the luminance of the displayed color picture canmaterially be increased.

Further object of the present invention is to realize a gas dischargedisplay panel using hollow cathodes being able to operate at a lowvoltage and thus to display a large size color picture in highefficiency.

Still further object of the present invention is to simplify theconstruction of the gas discharge display panel for color picturedisplay and to simplify machining of the parts or assembling of thepanel so that utilization of the display panel may be improved.

More particularly, the present invention has for its one object toarrange the hollow cathode used in the gas discharge display panel to besuitably dimensioned so that a high luminance gas discharge displaypicture can be reproduced at low voltage.

The gas discharge display panel using hollow cathodes according to thepresent invention has a construction in that three discharge units forrepresenting three primary colors red, green, blue and forming onepicture element are arranged to couple against one scanning hollowcathode as one set of the units, that the hollow cathode is so arrangedto operate partly as a discharge display unit and partly as a scanningunit for initiating the display discharge, and that slots are providedat back side of the intermediate. insulating panel provided with thehollow cathode so as to connect said hollow cathodes in order totransmit the scanning discharge and to obtain a definite zigzag shapedinterlacing scanning and thus to produce a large size color picture ofhigh quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view indetached form of a conventional gas discharge display panel;

FIG. 2 is a detached perspective view of a gas discharge display panelaccording to the present invention;

FIG. 3 is a diagram for showing the scheme of transition of plasmapositions in zigzag form interlaced scanning;

FIG. 4 shows waveform diagrams for showing various driving voltages foreffecting said interlaced scanning;

FIG. 5 is a diagram for explaining disposition of red, green. blue unitsforming one picture element in the display panel according to thepresent invention;

FIG. 6 is a diagram for explaining relative position between the hollowdisplay cathode and the hollow scanning cathode;

FIG. 7 is a diagram for explaining a different relative positionsbetween said two cathodes;

FIG. 8 is a perspective view showing construction of a hollow scanningcathode provided with slots for supplying seed discharge;

FIG. 9 is an explanatory view for showing relative position of thehollow scanning cathode shown in FIG. 8 and the hollow display cathode;

FIG. 10 is a diagrammatic cross-sectional view of the hollow cathodeused in a gas discharge display panel of the present invention; and

FIG. 11 shows characteristic curves for showing discharge current (Ie)to discharge voltage (Vd) characteristics in comparison between a knowndischarge cell (I) and two discharge cells according to the presentinvention (II and III).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now beexplained in more detail be referring to the accompanied drawings. Oneembodiment of the gas discharge display panel for color picturereproduction according to the present invention is shown in FIG. 2 indetached form. Referring to FIG. 2, the gas discharge display panelcomprises a front panel 21 formed by transparent insulating materialsuch as glass and a first intermediate-insulating plate 22 made ofinsulating material such as glass or ceramic. On the inner surface ofthe front panel 21 a number of display anode stripes 23 are provided inparallel. In the present embodiment the stripes 23 are providedvertically. These stripes 23 may alternatively be provided on the frontsurface of the first intermediate insulating plate I 22. A great numberof small holes 24 are provided in the first intermediate insulatingplate 22 in matrix form. The holes 24 and the display anode stripes 23are arranged to face oppositely each other. On the wall surface of thesmall holes 24 conductive materials are applied by means of printing,vaporization, metallization or soldering or the like to form hollowdisplay cathode 24' having from opening. Each two lateral rows of thesehollow display cathodes 24' are connected together by a conductivestripe 25 provided on the back surface of the first intermediateinsulating plate 22 in a direction normal to the direction of thedisplay anodes 23.

The gas discharge display panel further comprises a second intermediateinsulating plate 26 made of insulating materials such as glass orceramics and a rear panel 30 also made of insulating materials such asglass or ceramics. The second intermediate insulating plate 26 comprisesa plurality of hollow scanning cathodes 27 each formed by a small holeand provided at a position facing against a set of three hollow displaycathodes 24. The hollow scanning cathodes 27 are connected by conductivestripes 28 being provided in parallel on the front surface of the secondintermediate in,- sulating plate 26 at positions against respectiveconductive stripes 25 connecting said hollow display cathodes 24 foreach two rows. The hollow scanning cathodes 27 are arranged in a form ofsubstantially regular matrix shaped at a pitch corelated to theallocation of the hollow display cathodes 24 as has been describedbriefly in above and will more fully be described hereinafter. Innersurface of the hole forming the hollow scanning cathode 27 andperipheries of its front opening are coated by conductive material bymeans of printing, vaporization, metallization or electroplating, etc.The front openings of the scanning cathodes 27 in one column areconnected by a conductive stripe 28 as mentioned above. Rear sides ofthe hollow scanning cathodes 27 are connected together by scanning slots29 running curved shaped or zigzag shaped and generally normal to thedirection of said conductive stripes 28. On the front surface of therear panel 30, a plurality of scanning anodes 31 are provided inparallel and in a direction normal to the conductive stripes 28connecting the hollow scanning cathodes 27 by means of printing.vaporization, metallization or electroplating, etc. The scanning anodes31 are formed in stripe shaped or belt shaped by applying conductivematerial. To each of the scanning anode 31, there is provided withconnecting wire 32.

The front panel 21, the first intermediate insulating plate 22, thesecond intermediate insulating plate 26 and the rear panel 30 arestacked together in this sequence to form a united display panel in thesame manner as of the conventional type. Peripheries of the panel aresealed air tightly, and rare gas, such as, helium. neon, argon, xenon orthe like or mixture with nitrogen or hydrogen thereof is introducedafter evacuation. The pressure of the sealed gas is for example severaltens to several hundreds Torr and the composition of the sealing gas isso selected as to produce maximum ultraviolet ray irradiation. On theinner surface of the front panel 21, phosphorescent material is coatedat respective positions opposite to the hollow display cathodes.

The allocation of the phosphorescent coating films R, G and Birradiating three primary colors, red, green, blue, respectively, andforming one picture element is selected for instance as shown in FIG. 5.In this arrangement. each picture element is arranged at location havingequidistant pitch both'in vertical and in horizontal directions. Thephosphorescent film of each color is arranged at a pitch of 3:2 invertical and in horizontal directions. The relative position of thehollow display cathodes 24, each of which corresponds to one of a set ofthree primary color phosphorescent films forming one picture element,against the hollow scanning cathode 27 is as shown in FIG. 6. Namely,one hollow scanning cathode and three hollow display cathodes areoverlapped to form three small through holes g which can be observedthrough the front panel 21. In other words the three hollow displaycathodes 27 forming one set of picture element are arranged in partlyoverlapping position with a hollow scanning cathode 27 which is providedcommonly with the set of three cathodes 27. The through holes 3 formedby said overlapping portions have been provided under an object tosupply the seed discharge produced at the scanning anode side to thedisplay anode side. A particular feature of the panel according to thepresent invention is the fact that the seed discharge is supplied fromone hollow scanning cathode to the three hollow display cathodessimultaneously of which cathodes forming a set of three groups for red,green and blue luminance.

The seed discharge between the sanning anode 31 and the hollow scanningcathode 27 for causing the display discharge moves in zigzag form asshown in FIG. 2 by means of a combination of driving waveforms ofscanning anode driving amplifier (not shown) and scanning cathodedriving amplifier and also by a combination of scanning slot 29 andadjacent cathode. In this respect, at each location where the seeddischarge had been transferred, the respective seed discharge issupplied to the side of hollow display cathode 24 via the respectivethrough holes at the location of superposition for each of red, greenand blue luminance as shown in FIG. 6. The cross-sectional area Sg m'r'T of the portion of one common through hole g must be so selected onone hand to be equal to or larger than 1r/4( l5)te)fn m for easyestablishment of the seed discharge, wherein Ae is mean free path ofelectron in the sealed gas, and on the other hand to be less thanonethird of the cross-sectional are Sd m of the hollow display cathode24 in order to minimize amount of ultraviolet ray radiation or visiblelight leaking from the display cathode 27 to the display panel side. Ifwe assume the diameter of the hollow cathode 24 to be Dd, when thecathode is a circular form, then Sd becomes as Sd 1r/4Dd' Under acondition that the seed discharge being supplied to the hollow displaycathode 24 through the through holes g formed in a manner mentioned. asabove, and that an output of a display anode driving amplifier beingsupplied to the display anodes R,, R R G,, G G 8,, B B,,, and furtherthat an output of a scanning driving amplifier being supplied to thecathode side, and the electrodes are excited by a combination of thedriving waveform, picture elements in one row at positions atintersections between the sets of display anodes having suffixes l, 2,3; 4, 5, 6; 7, 8, 9; 10, ll, 12;. and respective column of the scanningcathodes are successively selected and scanned in zigzag form. In thesucceeding frame, the rest of the picture elements are scanned alsozigzag shaped and as the result a color picture of one frame isreproduced.

For example, as shown in FIG. 3, by a first field scanning a zigzagshaped interlaced scanning in oblique direction with'the scanning anodesa, to a as shown by full line arrows is made and by a successive fieldscanning the same for scanning anodes b, to b, is made. The scanningwill more fully be explained by referring also to FIG. 4, in whichwaveforms of various driving voltages are shown. The scanning anodes 31are divided into two groups as shown in FIG. 2 and the groups areconnected to sources A, and A respectively. To these groups a pulse wavesignal C having binary value VA and VA and having period correspondingto one picture element interval is applied. The voltage VA in this caseis so selected as a necessary value to produce plasma definitely betweeneach of the scanning anode 31 and the scanning cathode 28 when thelatter is at zero potential. This voltage VA is for instance 250 V. Onthe other hand, the voltage VA is so selected as a voltage at which theaforementioned plasma extinguishes and further as a value at which adischarge is not produced between the groups of scanning anodes A, and AThis value VA is for instance V for the value of VA=25O V. In thismanner, by alternatively switching the output voltages of the voltagesources A, and A into values VA and VA, the discharge points move in adirection normal to the scanning anode, i.e., in Y-direction of FIG. 3.On the other hand, as shown in FIG. 4, the respective cathodes 28 areapplied with three phase pulse waveform signals synchronized with eachother at one picture element spacing and switching successively fromthree driving voltage sources 1b,, (b and 4) By these driving voltages,the discharge points move in the direction of the scanning anodes, i.e.,in Z-direction in FIG. 3. Accordingly, in combination with theabovementioned displacement in Y- direction by the driving voltagesources A, and A a zigzag shaped scanning in oblique direction with thescanning anodes 31 is realized. The value of the pulse waveform voltageVB applied with the cathodes 28 should be so chosen as to besufficiently low to turn off the discharge plasma at the scanning anode31 when the voltage VA is applied thereto. A pulse waveform signal 41 inFIG. 4 is reset pulse signal applied to a reset cathode R shown in FIG.2.

As for the disposition of the respective primary color discharge unitsin red, green, blue, besides of the embodiment shown in FIG. 5, it ispossible to dispose the respective discharge units at respective summitsof a triangle and to arrange the ratio of vertical and horizontalpitches for each discharge unit to be 2 3 :3 or l.l55z1, or to disposethe three discharge units in a relation of vertical to horizontal pitchratio in 1:4 or 1:2, respectively. The disposition shown in FIG. 5 hasequal picture element pitches in vertical and horizontal directions. inwhich the pitch for both directions is 3a, and an excellent picturequality is expected if compared with the abovementioned embodiments. Inaccordance with experiments made by the inventors, it has been confirmedthat a most excellent result in the visual view point is obtained whenthe ratio between an interval in the scanning direction and an intervalin a direction normal thereto for each picture element is defined in arange more than 0.87 and less than 1.15.

FIGS. 7a and 7b show different embodiments being applied minormodification of the configuration of the picture elements. The botharrangements have corresponding vertical and horizontal pitches withthose shown in FIG. 5. FIG. 7a shows an embodiment in which each unitcoated at inside of the front panel is made in elliptic shape. FIG. 7bshows an embodiment in which each unit is made in square shape. Thepicture quality of these embodiments is equivalent to that shown in FIG.5 and the size of the picture elements can be enlarged in the directionof the display anodes 23.

In the foregoing explanation. the gas discharge display panel of thepresent invention has been described to comprise respective primarycolor display hollow cathodes 24 of red. green and blue for eachscanning hollow cathode 27. FIG. 8 shows a different embodiment fromthat shown in FIG. 2. In the figure. only the second intermediateinsulating plate 26 provided with the scanning hollow cathodes 27 isshown separately. In this embodiment, the display hollow cathodes 24 andthe scanning hollow cathodes 27 are arranged in a relative position ascan be seen from FIG. 9. In FIGS. 8 and 9, outwardly projecting grooves29 from the cylindrical scanning hollow cathode 27 are provided to formthrough holes for supplying the seed discharge from the scanning side tothe display side. The cross-sectional area Sg Fri m of the through holeportion in the overlapped area of the hollow cathode between thescanning side and the display side is defined in the same manner withthe foregoing embodiment as in the following range.

When defining the cross-sectional area of the through hole portion inthe overlapped portion of the hollow cathode between the scanning sideand the display side, the cross-sectional area of the hollow cathodebeing a base of such calculation is defined in a line of followingconsideration both for the scanning side and the display side.

FIG. 10 shows just a schematical cross-sectional view of such hollowcathode used in the gas discharge display panel. By referring to FIG. 10the operation of the gas discharge display panel and that of the hollowcathode 41 will be explained. Generally, in a gas discharge displaypanel. a gas such as neon. helium, argon, cripton, xenon. hydrogen,nitrogen or mercury. etc., is sealed inside at a suitable gas pressurefor maintaining a stable glow discharge. In the operation, two kinds ofphenomena exist in combination. The one of them is to selectivelytransmit glow discharge to the scanning anode 43 arranged on the rearpanel 46 adjacent to the cathode. The other one is to derive the glowdischarge produced between the cathode 41 and the scanning anode 43 tothe side of the display anode 42 arranged on the front panel 45 inaccordance with the signal to be displayed and to obtain the display bycausing the luminant discharge.

In the self-scanning type gas discharge display panel as shown in FIGS.1 and 2, at first the reset cathode R is earthed for a period forproviding an ignition discharge thereof, then the cathode is earthed ata certain period corresponding to phase 4), and the reset cathode R isreturned to the potential of voltage value +VB. In this situation, thecathode in phase (I), located adjacent to the reset cathode R dischargesat top priority and the glow discharge is transferred from the resetcathode R to the cathode in phase 4),. During the period in which thedischarge is maintained at the cathode of phase 41., the other cathodeswill not cause discharge due to voltage drop by the discharge current sothat the discharge is not transferred. At the next period cathode inphase (b is earthed and phase d), cathode is returned to the potential+VB and under the same selective condition as mentioned above. the glowdischarge is now transferred to the cathode in phase da- In the samemanner. the successive cathode in phase (11 and so on will be earthedsuccessively and the glow discharge will be transferred in turn.

The brightness obtained by the luminous discharge in the gas dischargedisplay panel has been confirmed to increase in proportion to anincrease of the discharge current. When the cathode is formed by aconductor stripe, only a weak discharge current can be supplied due toits small working surface and it may require to operate the dischargecell in a range of abnormal glow if a practical high brightness isdesired. But in this case, as mentioned above, an inconvenience mightoccur by the increase of the discharge voltage, for instance, to causean erroneous discharge to an adjacent discharge cell.

The cathode need not be made in plate shape as has been explained in theforegoing. As shown in FIG. 10, an intermediate plate 47 is providedwith regularly arranged matrix holes. The inner side of the holes may becoated with conductive materials. such as for instance, gold, platinum,nickel, iron, cobalt, molybdenum, tin, aluminum or iron-nickel alloy toform hollow cathodes 41. A plurality of such hollow cathodes 41 areconnected together by means of a conductive film 44 so as to form thecathode groups. The size of the hollow cathode 41 of this embodiment canbe decided by the following manner.

Usually a gas discharge display panel operates in a normal glowdischarge condition depending upon a certain pressure of the sealed gasand the current density .I K at the cathode surface is maintainedconstant. In

this condition. the current density .lK dominates the space chargedensity of the cathode' dark space or the Crookes dark space located infront of the cathode. The mean number of collision between electrons andmolecules in thecathode dark space under this condition is equal tod/ke, wherein (1 is the thickness of the cathode dark space and M is themean free path of electrons. The value of d/Ae is about 9 to 24. On theother hand, it is known that in case of such a cylindrical hollowcathode 41. the best hollow cathode discharge 7 effect or hollow effectcan be obtained under the condition of D=2d, wherein D is the innerdiameter of the cylindrical electrode 41 by taking into account thefront portion of the cathode during the discharge condition. Thiscondition 1) 2d corresponds to a case in which the negative glowdischarges produced along the inner surface of the hollow cylindricalcathode unit together as can be seen from FIG. 10. In other words, it ispossible to lower the discharge maintaining voltage and to increase thecathode current under this condition. Therefore by realizing thiscondition. it is possible to increase the brightness of the picture tobe displayed and to decrease blackening of the panel.

The inventors of the present application had carried an extensiveexperiments for clarifying these phenomena by sealing neon gas in anexperimental discharge panel provided with hollow cylindrical cathodes.The

inventors had found that a remarkable hollow effect and D/he 150wherein,

kc is the means free path of an electron,

D is the inner diameter of the hollow electrode,

L is the length of the electrode.

The size of the hollow cathode in the gas discharge display panelaccording to the present invention is basically decided by the aboveequations based on thevarious experiments.

A comparison for discharge voltage to discharge current characteristicsbetween gas discharge display panels according to the present inventionand a conventional gas discharge display panel comprising a platecathode is shown in FIG. II. In FIG. 11, curve I represents acharacteristic curve of a conventional panel having a plate cathode inwhich the discharge voltage Vd shows a remarkable increase according toan increase of the discharge current le. Curve II shows a characteristiccurve of a display panel according to the present invention havinghollow cathodes of inner diameter d and curve III shows that of furtherembodiment of the present invention in which said inner diameter is d Ascan be seen from the curves II and III. the display panels of thepresent invention show a very little increase of the discharge voltageVd. More especially in the embodiment having the diameter d shown incurve [I] shows an excellent characteristic in which the dischargevoltage V11 is substantially constant at an increase of the dischargecurrent Ie.

In case of the respective primary color discharge units are arranged ina shape as shown in FIG. 7. the oblong formed hollow scanning cathodeshown by dotted line or one as shown by 27 in FIG. 9 which comprises 3projected corners may be used. The crosssectional area of theabovementioned through holes g where the cross-section is not a circlecan be defined in substantially same manner with that mentioned in theabove. In this case, the cross-section of a hollow cathode issubstituted in calculation with a circle having the same surface area.If the hollow cathode is formed in a frustconical shape in order toenlarge the area of phosphorescent film excited by the ultravioletirradiation produced by the discharge plasma or to enlarge the apparentarea of the phosphorescent coating viewed from the front side, thecross-sectional area of the through hole portion should be calculatedagainst an effective area of the hollow cathode at as intersection ofthe scanning side and the display side of the hollow cathode.

The gas discharge display panel for color picture reproduction accordingto the present invention can realize a high fill factor arrangement ofthe primary color picture elements and is able to reproduce a highdefinition color picture. On the other hand, the panel. especially inthe embodiments showns in FIG. 7a or 711. which comprises oblong orelongated primary color discharge units closely arranged together at avery high fill factor. has at the same time a certain danger to causeerroneous discharge between a scanning hollow cathode and adjacentprimary color discharge unit through gaps between intermediateinsulating plates so as to result a cross-talk.

In order to avoid such malfunction in the gas discharge display panelaccording to the present invention. the whole area between layers wheresuch erroneous discharge might cause, for instance. between the twointermediate insulating layers may be sealed except the portion formingthe discharge path instead of sealing only the peripheries of thestacked layers forming a display panel. By such whole area sealing, thecrosstalk due to erroneous discharge can be prevented. In case ofinsulating layers are made of glass, thin flit glass may be coated onthe whole surface between such layers and the layers may be pressedtogether while heat- As has been mentioned above, the gas dischargedisplay panel according to the present invention is formed to operatethe hollow cathode separately for the scanning anode side and for thedisplay anode side. One scanning hollow cathode is combined with a setof display hollow cathodes. The seed discharge produced by one plasmaoccurring between a pair of discharge electrodes consisting of ascanning anode and a scanning cathode is divided so as to supply theexcitation energy to the plurality of display anodes. Furthermore. theholes which supply the seed discharge from the scanning anode side tothe display anode side are formed by very small through holes only to beviewed through by the viewer. Therefore the major portions of the holeare not throughly overlapped.

In the gas discharge display panel according to the present invention,the vertical and horizontal pitches of each primary color pictureelement for displaying the three primary colors can more freely beselected in a suitable ratio if compared with the gas discharge displaypanel of the conventional type. Further it affords an improvement in theconstruction of the scanning hollow cathode itself and the arrangementof combination for the scanning hollow cathode and the display hollowcathode. Thus the display panel according to the present invention hasan advantage to be able to display an excellent picture at a highcontrast ratio in color. In the gas discharge display panel according tothe present invention, one scanning hollow cathode is arrangedoppositely with a set of three display hollow cathodes for reproducingthe three primary colors so that the arrangement and construction of thescanning hollow cathodes becomes much more simpler if compared with theconventional arrangement. which may afford many practical advantages.

What we claim is:

l. A gas discharge display panel comprising in combination;

a front panel formed by transparent insulating material,

a first intermediate insulating plate provided with a plurality ofpicture elements arranged in matrix shape. in which each picture elementis formed by a set of three display discharge units for displaying threeprimary colors, red. green and blue. respectively. and each of thedisplay discharge unit comprises a hollow display cathode.

a number of display anode stripes extended in parallel and providedbetween the front panel and the first intermediate insulating plate, inwhich the display anode stripes are formed in groups for respectiveprimary colors and each stripe being provided at a location to establishregistration with respective row of said display discharge units forreproducing corresponding primary color,

a second intermediate insulating plate provided with a plurality ofhollow scanning cathodes, in which each hollow scanning cathode isprovided at a position facing against said set of hollow displaycathodes representing a picture element and each column of the hollowscanning cathodes are connected by a conductive stripe,

a rear panel made of insulating material, and

a plurality of scanning anodes provided in parallel on the rear panel ina direction normal to said conductive stripes,

wherein the set of the hollow display cathodes and the hollow scanningcathode are so arranged as to overlap at through holes having smallcrosssectional area so that a scanning discharge produced between thescanning cathode and the scanning anode can easily be transferred to thehollow display cathode forming the display discharge unit together withthe display anode in a manner that the scanning discharge will not givesubstantial influence to a viewer located at the front panel side.

2. A gas discharge display panel according to claim 1, wherein thedisplay anode stripes are provided on inner surface of the front panel.

3. A gas discharge display panel according to claim 1, wherein thedisplay anode stripes are provided on front surface of the firstintermediate insulating plate.

4. A gas discharge display panel according to claim 1, wherein thehollow scanning cathodes are connected at part of its rear side by slotsprovided in said second intermediate insulating panel.

5. A gas discharge display panel according to claim 1, wherein across-section of the scanning hollow cathode shows three outwardlyprojecting grooves and each groove overlaps with one of the hollowdisplay cathode in its cross-section to form a through hole.

6. A gas discharge display panel according to claim 5, whereincross-sectional area Sg of the through holes of a hollow scanningcathode is selected with respect to mean free path of electron of sealedgas and crosssectional area Sd of the hollow display cathode in a rangeof following equation,

7. A gas discharge display panel according to claim 5, wherein thecross-sectional area Sd of the hollow display cathode and length L ofthe same are selected with respect to diameter D of a circle havingcorresponding area Sd and with the electron mean free path he in a rangedefined by the following equation,

15 D/Ae and 8. A gas discharge display panel according to claim 1,wherein said sets of hollow display cathodes are arranged in lateral toverticalpitch ratio between 0.87 to 9. A gas discharge display panelaccording to claim 8, wherein said hollow display cathodes are made in aform selected from circle, oblong circle. elongated square shape andbeing made in substantially same cross-sectional area.

10. A gas discharge display panel according to claim 9, wherein saidhollow scanning cathodes are obliquely connected in a groupcorresponding to even number row by said slot so as to cause zigzagshaped interlaced scanning.

1. A gas discharge display panel comprising in combination; a frontpanel formed by transparent insulating material, a first intermediateinsulating plate provided with a plurality of picture elements arrangedin matrix shape, in which each picture element is formed by a set ofthree display discharge units for displaying three primary colors, red,green and blue, respectively, and each of the display discharge unitcomprises a hollow display cathode, a number of display anode stripesextended in parallel and provided between the front panel and the firstintermediate insulating plate, in which the display anode stripes areformed in groups for respective primary colors and each stripe beingprovided at a location to establish registration with respective row ofsaid display discharge units for reproducing corresponding primarycolor, a second intermediate insulating plate provided with a pluralityof hollow scanning cathodes, in which each hollow scanning cathode isprovided at a position facing against said set of hollow displaycathodes representing a picture element and each column of the hollowscanning cathodes are connected by a conductive stripe, a rear panelmade of insulating material, and a plurality of scanning anodes providedin parallel on the rear panel in a direction normal to said conductivestripes, wherein the set of the hollow display cathodes and the hollowscanning cathode are so arranged as to overlap at through holes havingsmall cross-sectional area so that a scanning discharge produced betweenthe scanning cathode and the scanning anode can easily be transferred tothe hollow display cathode forming the display discharge unit togetherwith the display anode in a manner that the scanning discharge will notgive substantial influence to a viewer located at the front panel side.2. A gas discharge display panel according to claim 1, wherein thedisplay anode stripes are provided on inner surface of the front panel.3. A gas discharge display panel according to claim 1, wherein thedisplay anode stripes are provided on front surface of the firstintermediate insulating plate.
 4. A gas discharge display panelaccording to claim 1, wherein the hollow scanning cathodes are connectedat part of its rEar side by slots provided in said second intermediateinsulating panel.
 5. A gas discharge display panel according to claim 1,wherein a cross-section of the scanning hollow cathode shows threeoutwardly projecting grooves and each groove overlaps with one of thehollow display cathode in its cross-section to form a through hole.
 6. Agas discharge display panel according to claim 5, whereincross-sectional area Sg of the through holes of a hollow scanningcathode is selected with respect to mean free path of electron of sealedgas and cross-sectional area Sd of the hollow display cathode in a rangeof following equation, pi /4(15 lambda e)2 < or = Sg < or = (Sd/3).
 7. Agas discharge display panel according to claim 5, wherein thecross-sectional area Sd of the hollow display cathode and length L ofthe same are selected with respect to diameter D of a circle havingcorresponding area Sd and with the electron mean free path lambda e in arange defined by the following equation, 15 < D/ lambda e < 150 and 2 <D/L <
 15. 8. A gas discharge display panel according to claim 1, whereinsaid sets of hollow display cathodes are arranged in lateral to verticalpitch ratio between 0.87 to 1.15.
 9. A gas discharge display panelaccording to claim 8, wherein said hollow display cathodes are made in aform selected from circle, oblong circle, elongated square shape andbeing made in substantially same cross-sectional area.
 10. A gasdischarge display panel according to claim 9, wherein said hollowscanning cathodes are obliquely connected in a group corresponding toeven number row by said slot so as to cause zigzag shaped interlacedscanning.